Multi-passage oil debris monitor to increase detection capability in high oil flow systems

ABSTRACT

An oil debris monitoring sensor includes a multiple of passages within the housing, each of the multiple of passages surrounded by a set of coils to detect a particle. A method for determining a presence of a particle in a system includes a) installing a single sensor in-line with an oil flow path; b) communicating oil through a multiple of passages within the housing of the single sensor; c) detecting a particle through the single sensor; and d) isolating the particle to one of the multiple of passages within the sensor housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/456,420, filed Jun. 28, 2019.

BACKGROUND

The present disclosure relates to an oil system for rotating machinerysuch as a gas turbine engine and, more particularly, to a multi-passageoil debris monitoring sensor.

Many types of mechanical machinery include various components thatrequire lubrication. Gas turbine engines, for example, typically includegears and bearings that require a lubricating liquid, such as oil, forlubrication and cooling during operation. When an oil wetted componenthas a mechanical failure, metallic debris may be released into thelubricating liquid. In order to receive advanced warning of thesemechanical systems failures for the purpose of condition-basedmaintenance, lubrication systems may include an oil debris monitoringsystem to sense metallic debris in the oil. An oil debris monitor systemis used to flag the initiation or progression of mechanical failures inthe lubricated mechanical machinery.

Metallic debris, measured by the counts and mass of particles detectedby the oil debris monitor, is processed and monitored by a controller,and when debris is released at a critical rate, an alert is produced,driving field troubleshooting and corrective action. While oil debrismonitor sensing technology is well developed, application of thistechnology in aerospace systems, such as gas turbine engines, is muchchallenged due to the stringent requirements on fault detection and theenvironment.

Today's aerospace systems are often built with great sophistication andlittle margin, which requires fault detection to be early, accurate andreliable. For mechanical failures in gas turbine engine applications,detection of fine particles (a few hundred microns) is required. Theoperating environment (vibration, pressure pulsations, aeration, etc.)can induce noise in oil debris monitor signals. Furthermore, the ODMsensor detection capability is defined by signal to noise ratio (SNR).SNR is defined by sensor oil flow bore cross sectional area for a givenparticle size. As thrust requirements for engine scale upward, the oilflow requirement also increases to ensure adequate system cooling. Toprevent an ODM sensor from choking the system as oil flow increases,sensor bore has historically been increased to fit into the lubricationsystem. A sensor with an increased bore, however, will eventually nolonger be able to detect small particles and the SNR for the same sizedparticle will continually decrease as bore size increases. This may alsoprevent enough debris in a failure mode from being detected foreffective condition-based maintenance capability. A potential solutionto this problem would be to install two ODM sensors in the system inparallel. Although this method can be used to meet the detectionrequirements for a system, it also doubles the weight, cost, andcomplexity of the sensors and harnesses, and plumbing. Furthermore, thescalability of this concept is limited (i.e., three or more sensorsbecomes exceedingly uneconomical).

SUMMARY

An oil debris monitoring sensor according to one disclosed non-limitingembodiment of the present disclosure includes a multiple of passageswithin a housing, each of the multiple of passages surrounded by a setof coils required for particle detection.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that the multiple of passages within the housingincludes two or more passages.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that a first set of coils around a first passage ofthe multiple of passages are wound in a different direction than asecond set of coils around a second passage of the multiple of passages.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes a dielectric between the first passage and thesecond passage.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that each set of coils includes a respective firstfield coil, a sensor coil, and a second field coil.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that the housing is located in-line with an oil flowpath that is in communication with a geared architecture of a gasturbine engine.

An oil debris monitoring sensor according to one disclosed non-limitingembodiment of the present disclosure includes a first passage within ahousing along a first axis; a first field coil, a sensor coil, and asecond field coil around the first passage and along the first axis; asecond passage within the housing along a second axis parallel to thefirst axis; and a first field coil, a sensor coil, and a second fieldcoil around the second passage and along the second axis.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that the housing is located in-line with an oil flowpath that is in communication with a geared architecture of a gasturbine engine.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that a first magnetic field generated by the firstfield coil around the first passage is in a first direction and a secondmagnetic field generated by the first field coil around the secondpassage is in a second direction opposite the first direction.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes a dielectric between the first passage and thesecond passage.

A method for determining a presence of a particle in a system accordingto one disclosed non-limiting embodiment of the present disclosureincludes: a) locating a housing in-line with an oil flow path; b)communicating oil through a multiple of passages within the housing; c)detecting a particle through processing data from each passage; and d)isolating the particle to one of the multiple of passages within thehousing.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes locating the oil flow path in communication with ageared architecture of a gas turbine engine.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that step d) includes generating a first magneticfield around a first passage in a first direction and generating asecond magnetic field around a second passage in a second directionopposite the first direction.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that step d) includes determining an interferencebetween a magnetic field associated with a first passage and a magneticfield associated with a second passage in response to the particlepassing through the housing.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that step d) includes applying a channel isolationalgorithm if a minimum voltage is not identified in response to theparticle passing through the housing.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that step d) includes applying a channel isolationalgorithm if a minimum voltage is not identified.

A further embodiment of any of the foregoing embodiments of the presentdisclosure includes that step d) includes determining whether a minimumamplitude in a second passage is within a predetermined range, andassessing whether a second particle is passing through the secondpassage.

The foregoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated otherwise.These features and elements as well as the operation thereof will becomemore apparent in light of the following description and the accompanyingdrawings. It should be appreciated; however, the following descriptionand drawings are intended to be exemplary in nature and non-limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art fromthe following detailed description of the disclosed non-limitingembodiments. The drawings that accompany the detailed description can bebriefly described as follows:

FIG. 1 is a schematic cross-section of an example gas turbine enginearchitecture.

FIG. 2 is a schematic cross-section of a geared architecture for a gasturbine engine.

FIG. 3 is a schematic diagram of an oil system for a geared architecturegas turbine engine.

FIG. 4 is a schematic diagram of a debris detection system according toone disclosed non-limiting embodiment.

FIG. 5 is a schematic view of a multi-passage oil debris monitoringsensor.

FIG. 6 is a schematic cross-section of the multi-passage oil debrismonitoring sensor of FIG. 5 with two passages.

FIG. 7 is a schematic cross-section of the multi-passage oil debrismonitoring sensor with multiple passages.

FIG. 8 is a representation of the field coil magnetic field directionsof the multi-passage oil debris monitoring sensor of FIG. 5 with twopassages.

FIG. 9 is a signal representation of a particle passing through passageone only of the FIG. 8 multi-passage oil debris monitoring sensor ofFIG. 5 with two passages.

FIG. 10 is a signal representation of a particle passing through passagetwo only of the FIG. 8 multi-passage oil debris monitoring sensor ofFIG. 5 with two passages.

FIG. 11 is a signal representation of a particle passing through bothpassages of the FIG. 8 multi-passage oil debris monitoring sensor ofFIG. 5 with two passages.

FIG. 12 is a signal representation of a larger particle passing throughpassage one of the FIG. 8 multi-passage oil debris monitoring sensor ofFIG. 5 with two passages.

FIG. 13 is a block diagram representative of logic for the multi-passageoil debris monitoring sensor.

FIG. 14 is a schematic representation of a calculated interference at anexample point C in between two magnetic fields of the multi-passage oildebris monitoring sensor of FIG. 5 with two passages.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26, and a turbine section 28. The fan section 22drives air along a bypass flowpath while the compressor section 24drives air along a core flowpath for compression and communication intothe combustor section 26, then expansion through the turbine section 28.Although depicted as a turbofan in the disclosed non-limitingembodiment, it should be appreciated that the concepts described hereinmay be applied to other engine architectures such as turbojets,turboshafts, and three-spool (plus fan) turbofans.

The engine 20 generally includes a low spool 30 and a high spool 32mounted for rotation about an engine central longitudinal axis Xrelative to an engine static structure 36 via several bearings 38. Thelow spool 30 generally includes an inner shaft 40 that interconnects afan 42, a low pressure compressor (“LPC”) 44 and a low pressure turbine(“LPT”) 46. The inner shaft 40 drives the fan 42 directly or through ageared architecture 48 that drives the fan 42 at a lower speed than thelow spool 30. An exemplary reduction transmission is an epicyclictransmission, such as a planetary or star gear system.

The high spool 32 includes an outer shaft 50 that interconnects a highpressure compressor (“HPC”) 52 and high pressure turbine (“HPT”) 54. Acombustor 56 is arranged between the high pressure compressor 52 and thehigh pressure turbine 54. The inner shaft 40 and the outer shaft 50 areconcentric and rotate about the engine central longitudinal axis X whichis collinear with their longitudinal axes.

Core airflow is compressed by the LPC 44, then the HPC 52, mixed withthe fuel and burned in the combustor 56, then expanded over the HPT 54and the LPT 46 which rotationally drive the respective high spool 32 andthe low spool 30 in response to the expansion. The shafts 40, 50 aresupported at a plurality of points by bearings 38 within the staticstructure 36.

With reference to FIG. 2, the geared architecture 48 includes a sun gear60 driven by a sun gear input shaft 62 from the low spool 30, a ringgear 64 connected to a ring gear output shaft 66 to drive the fan 42 anda set of intermediate gears 68 in meshing engagement with the sun gear60 and ring gear 64. Each intermediate gear 68 is mounted about ajournal pin 70 which are each respectively supported by a carrier 74.The input shaft 62 and the output shaft 66 counter-rotate as the sungear 60 and the ring gear 64 are rotatable about the engine centrallongitudinal axis X. The carrier 74 is grounded and non-rotatable eventhough the individual intermediate gears 68 are each rotatable abouttheir respective axes 80. An oil recovery gutter 76 is located aroundthe ring gear 64. The oil recovery gutter 76 may be radially arrangedwith respect to the engine central longitudinal axis X.

A replenishable film of oil, not shown, is supplied to an annular space72 between each intermediate gear 68 and the respective journal pin 70.One example applicable oil meets U.S. Military SpecificationMIL-PRF-23699, for example, Mobil Jet Oil II manufactured by ExxonMobilAviation, United States. Oil is supplied through the carrier 74 and intoeach journal pin 70 to lubricate and cool the gears 60, 64, 68 of thegeared architecture 48. Once communicated through the gearedarchitecture 48 the oil is radially expelled through the oil recoverygutter 76 in the ring gear 64 by various paths such as oil passage 78.

With reference to FIG. 3, an oil system 80 is schematically illustratedin block diagram form for the geared architecture 48 as well as othercomponents which receive oil. It should be appreciated that the oilsystem 80 is but a schematic illustration and is simplified incomparison to an actual oil system. The oil system 80 generally includesan oil tank 82, a supply pump 84, an oil debris monitoring sensor 86, anoil filter 88, a starter 90, a fuel pump 92, the geared and bearingarchitecture 48, a scavenge pump 94, and an oil debris monitoring sensor96 at an alternative location. The oil debris monitoring sensor 86, 96could be a single sensor or a set of sensors placed in branched oilpaths. The oil flow to the geared and bearing architecture 48 may beconsidered an oil supply path 100, and the oil flow from the geared andbearing architecture 48 can be considered an oil return path 102.Multiple of chip collectors 104 may be located in the supply path 100and the return path 102 to capture ferrous debris.

The sensors 86, 96 historically utilize two field coils, excited by highfrequency alternating current, to cause equal and opposing magneticfields (M-field). The ferrous particle strength of the M-field createdby one field coil after another, causes the processed signal to be aperiod of a sine wave. The nonferrous particle weakens the M-fieldcreated by one field coil after another, causing the similar sine wavebut in opposing polarity. Generally, the signal magnitude isproportional to the size of particle and the signal width is inverselyproportional to the particle speed.

With Reference to FIG. 4, a debris detection system 110 generallyincludes a controller 120 in communication with the sensors 86, 96. Thesensors 86, 96 may be in-line oil debris monitor sensors. The debrisdetection system 110 protects against unexpected phase angle changeswhich may affect individual oil debris monitors caused by replacement orredesign of other components in the system, such as a signal wireharness, that can drastically influence the phase angle.

The controller 120 generally includes a control module 122 that executeslogic 124 to actively calculate and monitor the oil debris liberated inthe oil system with regards to particle detection, mechanical systemfault alert, and sensing system health. The functions of the logic 124are disclosed in terms of functional block diagrams, and it should beappreciated that these functions may be enacted in either dedicatedhardware circuitry or programmed software routines capable of executionin a microprocessor-based electronics control embodiment. In oneexample, the control module 122 may be a portion of a flight controlcomputer, a portion of a Full Authority Digital Engine Control (FADEC),a stand-alone unit, or other system.

The control module 122 typically includes a processor 122A, a memory122B, and an interface 122C. The processor 122A may be any type of knownmicroprocessor having desired performance characteristics. The memory122B may be any computer readable medium which stores data and controlalgorithms such as the logic 124 as described herein. The interface 122Cfacilitates communication with other components such as the sensors 86,96, as well as remote systems such as a ground station, Health and UsageMonitoring Systems (HUMS), or other system.

The oil debris monitor phase angle is used to classify detected particletypes (ferrous/nonferrous) through a mathematical transformation. Thephase angle is calibrated by pulling a particle of known type and sizethrough the sensor and using the ratio of I and Q channel amplitude andtrigonometric relationships to calculate an optimum (for classification)phase angle. The I channel is the In-phase, or real component and the Qchannel is the Quadrature (90° shift of real component) to provide ahealth assessment that may include, for example, particle count,particle type classification, size and mass estimates, sensing systemavailability, debris count rates, and other metrics.

With reference to FIG. 5, the oil debris monitoring sensors 86, 96 eachgenerally include a housing 200 that contains a multiple of passages 202(two shown as A and B flow paths in FIG. 6 and seven shown as A-G flowpaths in FIG. 7). Each of the multiple of passages 202 are surrounded bya respective first field coil 210, a sense coil 212, and a second fieldcoil 214 along the axis of each. In the illustrated FIG. 6 example of atwo flow passage 202 arrangement, each flow passage 202 may have a setof field coils that are wound in opposing directions to minimize crosscoil interference between the A and B flow paths and also foralgorithmic isolation of particle path. Ideally, the generated magneticfields are of relatively equivalent magnitude and frequency (FIG. 8-12).

A reduced diameter sensor bore 212 increases the signal to noise ratiofor a given particle as compared to a larger bore and thereby increasesthe sensitivity to significantly smaller particles and achieves thiscapability without increasing the back pressure on the lube system tounacceptable levels for a given volumetric flow rate. This avoidsincreasing the differential pressure and producing a back pressure inthe system which exasperates active systems in the fluidic circuit.

A dielectric 216 may be located between one or more of the multiple ofpassages 202. The dielectric, intended to reduce or preventelectromagnetic interferences, may not completely shield the interactionbetween the magnetic fields around each bore. As such, some parsing canbe achieved by setting a minimum threshold in passage B based on theinfluence of the largest allowed particle in passage A and vice versa.If an excitation in passage B is greater than the above mentionedthreshold, a particle must be present. If an excitation is less than theminimum threshold, it must be a reflection of a particle passing throughchannel A. In other embodiments, isolation can be performed via pulsingthe field coils 210, 214 at different frequencies, staggering passagesthat cause deformation of the signal caused by the influence of theother passage, or combinations thereof.

With reference to FIG. 13, a method 300 for the management of theinteraction between the fields of the multiple of passages 202 so as toassure a proper count of particles that simultaneously pass throughmultiple passages of each oil debris monitoring sensor 86, 96 initiallyincludes excitation of the first and second field coil 210, 214 in eachof the multiple of passages 202 (302). Then, during operation, passageof one or more particles, any voltage imbalance is identified in thesense coil 212 in each of the multiple of passages 202 (304). Thevoltage imbalance data is then captured (306) and filtered (308). Thedata from the primary passage (e.g., the passage or lane through whichthe particle is passing, see FIGS. 9 and 10) is then processed withexisting proprietary algorithms (310).

A threshold is then applied (312) to determine the minimum voltage onone or more of the secondary passages to define if a particle is alsopassing through the one or more secondary passages (314) in addition tothe primary passage to properly identify the number of particles sensed.That is, whether multiple particles are passing though both passages(e.g., FIG. 11). or a single particle has passed through a single lane(e.g., FIG. 9, 10, 12). The ability to detect particles passing througha single sensor coil or multiple sensor coils depends on a threshold asdefined by a magnitude and other parameters that define the particlesignature (e.g., dashed horizontal lines in FIG. 9-12). This thresholdcan be determined by calibration of the system as it relates to thedetection requirements of the system. The threshold can be fixed by thelargest expected particle in system where the interference signal wouldbe no greater than the smallest particle that needs to be detected. Ifthere is system where the largest particle interference can be greaterthan the minimum detectable particle size, the minimum interferencethreshold can be adaptive to the dominant signal excitation (i.e. aparticle of given size X will generate an interface signal of no greaterthan Y on any other channel, where Y is a function of any X sense).

Finally, a channel isolation algorithm is applied if the minimum voltageis not identified (314). To ensure particle isolation to a specificpassage (assuming the primary passage has the particle) a minimumamplitude has to be detected in one or more secondary passages alongwith a range signal defining parameters matching to assess the signal inthe secondary passage to be a separate particle than that what is in theprimary passage (if signals are time aligned). In the case of adual-bore sensor, if a particle passes through a single channel, therewill be a threshold exceedance in the processed signal of that channel.Any interference may leak to the other channel, but is just a reflectionand does not breach the detection threshold (FIG. 9, 10, 12). If aparticle passes through both channels simultaneously, the minimumthreshold will be breached on each channel and the system will processthe data as if two particles are present (FIG. 11).

A particle entering field A (e.g., primary passage) will also bereflected in field B (e.g., secondary passage) as a form of what is seenin the primary passage (signal shape defined by set of parameters). Forexample, with reference to FIG. 14, the electromagnetic field created bythe field coils can be represented by Maxwell's third equation.

∇ × E = −∂B/∂t ${B\left( {x,y,z,t} \right)} = \begin{bmatrix}{{Bx}\left( {x,y,z,t} \right)} \\{{By}\left( {x,y,z,t} \right)} \\{{Bz}\left( {x,y,z,t} \right)}\end{bmatrix}$

At any axial point z0 and a given time t0, the magnetic flux can berepresented as a 2D vector as: B(x,y,z0,t0) . . . . Hence, the resultingmagnetic strength can be assessed and represented by a set of vectors ina given coordinate. Let A and B represent activated field coils creatinga magnetic field:

${B\left( {x,y,z,t} \right)} = \begin{bmatrix}{{Bx}\left( {x,y,{z0},{t0}} \right)} \\{{By}\left( {x,y,{z0},{t0}} \right)} \\{{Bz}\left( {x,y,{z0},{t0}} \right)}\end{bmatrix}$

The magnetic fields A and B produce interfering electromagnetic fieldsat an example point C such that resultant field at C will be the vectorsummation of the fields produced by A and B. This provides for themanagement of the interaction between the fields so as to assure aproper count of particles is provided should, for example, multipleparticles simultaneously travel through the passages.

The oil debris monitoring sensors 86, 96 enhance system capabilitywithin the confines of the existing space reducing the sensing coildiameter, increasing the signal to noise ratio for a given particle ascompared to a larger bore single sensor, increasing the sensitivity tosignificantly smaller particles, and achieve this capability withoutincreasing the back pressure in the system for a given volumetric flowrate. In addition, the sensor signal induced by interference from theother passage can be made much smaller than the signal due to particlepassage by virtue of the spatial relationship of the coils and byinstalling some degree of shielding. There may be still risk of missingdetection of small particles if a very large particle passes through thesystem simultaneously with a small particle, but the benefit of havingan un-intrusive sensor with adequate sensitivity for high thrust enginesoutperforms such risk, as a single large bore sensor detectioncapability loss is fixed and thus more severe. The oil debris monitoringsensors 86, 96 meets sensing capability, back pressure, weight, and thecost needs associated with sensing technology maturation for aviationapplications.

Although particular step sequences are shown, described, and claimed, itshould be appreciated that steps may be performed in any order,separated or combined unless otherwise indicated and will still benefitfrom the present disclosure.

The foregoing description is exemplary rather than defined by thelimitations within. Various non-limiting embodiments are disclosedherein; however, one of ordinary skill in the art would recognize thatvarious modifications and variations in light of the above teachingswill fall within the scope of the appended claims. It is therefore to beappreciated that within the scope of the appended claims, the disclosuremay be practiced other than as specifically described. For that reason,the appended claims should be studied to determine true scope andcontent.

1. A debris monitoring sensor, comprising: a housing; a first coil and asecond coil disposed in the housing; a first passage disposed in thefirst coil, the first passage configured to pass fluid for particledetection; and a second passage disposed in the second coil, the secondpassage configured to pass fluid for particle detection, wherein acentral axis of the first passage is parallel to a central axis of thesecond passage.
 2. The debris monitoring sensor as recited in claim 1,wherein the first passage and the second passage extend parallel throughthe housing.
 3. The debris monitoring sensor as recited in claim 1,wherein the first coil comprises a first set of coils around the firstpassage and the second coil comprises a second set of coils around thesecond passage, wherein the first set of coils is wound in a differentdirection than the second set of coils.
 4. The debris monitoring sensoras recited in claim 3, further comprising a dielectric between the firstpassage and the second passage.
 5. The debris monitoring sensor asrecited in claim 1, wherein the first coil and the second coil eachcomprises a respective first field coil, a sensor coil, and a secondfield coil.
 6. The debris monitoring sensor as recited in claim 1,wherein the housing is located in-line with an oil flow path that is incommunication with a gas turbine engine, and wherein the oil flow pathsplits between the first passage and the second passage in the housing.7. An oil system for rotating machinery, comprising: a rotating machine;an oil tank for storing oil for the rotating machine; a supply path forcarrying oil from the oil tank to the rotating machine; a return pathfor carrying oil from the rotating machine to the oil tank; a housingarranged along at least one of the supply path and the return path; anda multiple of parallel passages within the housing, each of the multipleof passages surrounded by a set of coils for particle detection.
 8. Thesystem as recited in claim 7, wherein the housing is located in-linewith the at least one of the supply path and the return path.
 9. Thesystem as recited in claim 7, wherein a first magnetic field generatedby a first field coil around a first passage of the multiple of passagesis in a first direction and a second magnetic field generated by a firstfield coil around a second passage of the multiple of passages is in asecond direction opposite the first direction.
 10. The system as recitedin claim 7, further comprising a dielectric between a first passage ofthe multiple of passages and a second passage of the multiple ofpassages.
 11. A method for determining a presence of a particle in asystem, comprising: a) locating a housing in-line with an oil flow path;b) communicating oil through a multiple of parallel passages within thehousing, the oil flow path dividing in parallel to flow through themultiple of parallel passages; c) detecting a particle throughprocessing data from each passage; and d) isolating the particle to oneof the multiple of passages within the housing.
 12. The method asrecited in claim 11, further comprising locating the oil flow path incommunication with a geared architecture of a gas turbine engine. 13.The method as recited in claim 11, wherein step d) comprises generatinga first magnetic field around a first passage in a first direction andgenerating a second magnetic field around a second passage in a seconddirection opposite the first direction.
 14. The method as recited inclaim 11, wherein step d) comprises determining an interference betweena magnetic field associated with a first passage and a magnetic fieldassociated with a second passage in response to the particle passingthrough the housing.
 15. The method as recited in claim 11, wherein stepd) comprises applying a channel isolation algorithm if a minimum voltageis not identified in response to the particle passing through thehousing.
 16. The method as recited in claim 11, wherein step d)comprises applying a channel isolation algorithm if a minimum voltage isnot identified.
 17. The method as recited in claim 11, wherein step d)comprises determining whether a minimum amplitude in a second passage iswithin a predetermined range, and assessing whether a second particle ispassing through the second passage.
 18. A method for determining apresence of a particle in a system, comprising: communicating oilthrough a multiple of passages within a housing; detecting a particle ina first passage of the multiple of passages through processing data fromthe one passage; and confirming the particle in the first passagethrough processing data from a second passage of the multiple ofpassages.
 19. The method of claim 18, wherein a first magnetic field isgenerated by a first coil set around the first passage and a secondmagnetic field is generated by a second coil set around the secondpassage, and wherein the data from the second passage comprises datarelated to impact of the particle in the first passage on the secondmagnetic field.
 20. The method of claim 18, wherein the multiple ofpassages comprise a multiple of parallel passages in the housing.